Power Wizard, PW18000, 110V Plug-In Electric Fence Charger, 18 Joule OutputPower Wizard shock technology plug-in models provide 110v of energy to contain cattle and keep predators out! Select a plug in model based on acreage, animal type and miles of wire. Whether you are protecting a single acre hobby farm or energizing wire fence to encompass 2,400 acres, there is a Power WizardUltra low impedance model to meet your needs.Additional Questions to Ask to Effectively Contain your Cows and other Farm AnimalsThere are a number of ways you can determine the right Power Wizard electric fence charger for your dairy farm, cattle ranch or hobby farm. Ask yourself:How many acres of my ranch will be enclosed by the electric fence? You will need to consider the size and shape of your farm. A square acre requires less miles of wire than a rectangular area of fencing.How many miles of wire were used to enclose the cattle or dairy cows? Most dairy farmers purchase their wire on spools 1/4 mile in length. How many spools were needed to enclose your cattle ranch?What output joules are required for the specific livestock; sheep, cows, cattle, etc.? The larger the animal and the larger the area enclosed, the more output joules are necessary.Predators are another consideration when building your electric fence. Energizing the top wire helps deter your dairy cows, beef cattle and other livestock from breaking through the fence and the powered lower wires will keep trespassers and predators like the feral hog from gaining access to your dairy farm, cattle ranch or hobby farm.